Conventionally, there is well known a multi-cylinder engine that each of the cylinders has a fuel injection valve. Such a multi-cylinder engine cannot obtain a stable driving state because of dispersion of rotation speed of each of the cylinders caused by specific dispersion of the fuel injection valves, structural tolerance of each of the cylinders, opening and closing timing of a suction and exhaust valve, or change with time of the engine. Then, there is also known an engine which controls fuel injection so as to reduce dispersion of rotation speed of each of the cylinders. The Japanese Patent Hei. 07-059911 discloses a control art of cylinders, whose order of combustion is continuous, that fuel injection amount of a certain cylinder is revised so as to make the maximum rotation speed equal to that of the cylinder just before at the time just after combustion.
However, dispersion of rotation speed may exist between each of the cylinders of the engine. By connecting load such as a hydraulic pump always to the engine, rotation alternation different from that following piston reciprocation of the engine may cause dispersion of rotation speed between each of the cylinders. The fuel injection amount revision control of the Japanese Patent Hei. 07-059911 is performed so as to make the maximum rotation speed of each of the cylinders equal to each other, whereby fuel injection amount may not be revised within the range of dispersion. In the case that the specific unevenness of rotation exists between the cylinders, when fuel amount is revised so as to make the rotation speed of each of the cylinders equal to each other, the specific alternation is also canceled, whereby it is disadvantageous because the fuel injection may be stopped or excessive injection may occur.